Signaling system



My l, 1945- N. D. NEWBY "a-r AL 2,374,884

SIGNALING SYSTEM Filed Aug. 19, 1945 5 sheets-'sheet 1 A TTORA/EV MS t HMH L nmvm 4 N.'D. NEwBY ETAL.

May '1, 1945.

' SIGNALING SYSTEM Filed Aug. 19, 194s 5 Sheets-Sheet 2 s /v. o. NEWB? h'. E. VAUGHA/v @M A TTONEY /N VEN TOR Gd K N www May 1, 1945.

N. D. NEWBY 'E1-AL 'SIGNALING SYSTEM Filed Aug; 19, 1945 y 5 Sheets-Sheet I5v mmm Sloa..

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May 1, i945.

N. D. NEwBY Erm.

's-IGNALING SYSEM.

Filed Aug. 1.9, '1943 5 Sheets-Sheet 4 /N VEA/rom N D. NEWBY H E. VAUGHAN ATTORNEY g May 1,'1945.

Y N. D. NEWBY Erm.

SIGNALING SYSTEM Filed Aug. 19, 1943 5 Sheets-Sheet 5 By, A @QW A Trop/VE v nals.

Patented May 1, 1945 UNITED STATES PATENT oFFlcs slcNslssssrs'rEM r Neal D. Newby,

Valley Stream,

Leonia, and Henry E. Vaughan,

N. Y., assignors to Bell Telev phone Laboratories, Incorporated, New York,

N. Y., a corporation of New .York

Application August 19, 1943, Serial No. 499,186

19 Claims.

This invention relates to signaling systems and particularly to telephone systems in which voice frequency currents are used for transmitting sig- Objects oi the linvention are the provision of more reliable signal transmitting and receiving means in systems employing voice' frequency signals and the provision of voice frequency signal transmitters and receivers arranged to prevent false operations in response to voice currents or other interfering currents.

. by a delay circuit impulse transmitting This invention is an improved signaling system comprising means for transmitting signals each of which consistsv of current impulses of three different frequencies in succession and to transmit' othersignals consisting of impulses of current of two of the three frequencies. The system. also comprises signal receiving means arranged to respond to said signals without responding to voice currents or other interfering currents. Similar signal `transmitting and receiving means are connected to each end of al telephone line, a different set of three frequencies being used for signaling in each direction thereover.

A feature of the invention is a signaling system comprising a signaltransmitter arranged to transmit seizure and answering supervisory signals consisting of an impulse ofcurrent of a rst frequency followed by an impulse of current of thesecond frequency; to transmit an enablement signal immediately preceding the transmission of selectiveon-hook and disconnect signals. the enablement signal consisting ofqan impulse of current of said second frequency followed by an impulse of current of said first frequency, each selective and on-hcok signal con-v sisting lof an impulse of current o f a third frequency for the duration of the signalfollowed by an impulse of current of said ilrst frequency, and each disconnect signal consisting of an impulse of said third frequency for a relatively long interval; and to transmit a disconnect acknowledgement signal consisting of an impulse of current of said second frequency followed by an impulse of current of said third frequency. The

transmitter is further arranged to repeat the transmission of a disconnect 'signal until an acknowledgment signal is received and to transmit the acknowledgment signal until no further disconnect signals are received.

A` further feature of the invention is a-signal constitute an enablement signal for preparing the line and signal receiving circuits at the other end of the toll line with which the signal transmitter is associated, the interval of time required for transmission of the' enablement signal prior to current of the third frequency being provided interposed between the signal receiving relay of the signal transmitter and the relays.

.Another feature of the invention is a signaling system comprising a signalreceiver arranged to .respond to signals of the character described without responding to voice currents or other interfering currents of the same frequencies -as those used for signaling.

These and other features of the invention Vwill be further described by considering a system embodying the invention, one such system being represented schematically in the drawingswhich form a partof this specification. The invention is not limited in its application to the particular system and circuit arrangements shown in the frequency signaling or telephone system.

Referring to the drawings: Figs. 1 and 2 show, in a rst toll omce, an operators position comprising a cord CDIfan outgoing trunk circuit OTI, a two-way trunk circuit TWTI, an incoming trunk circuit ITI, a signal transmitting circuit STI, a signal receiving circuit SRi and a toll line are associated with a to a second toll oilice;

Figs. 3, 4 and 5 show, in the second tollofflce, a toll line circuit TLC2, a signal receiving circuit SR2, a signal transmitting circuit ST2, a twoway trunk circuit TWT2, a selector circuit .TS2 and an outgoing trunk circuit 0T2, all individual to the toll line TLI2. Fig. 5 further shows an incoming trunk circuit IT! and an operators position comprising the cord circuit CD2; .and shows a toll selector T83, a two-way trunk circuit TWT3, an outgoing trunk circuit GT3, signal transmitterV ST3, signal receiver SRS, and toll circuit TLCI all of which toll line TLI2 extending line circuit 'I'LCB all associated with another toll line TLN extending to a third toll ofilce, and

Fig. 6 shows the relative positions in which Figs. l to 5 inclusive, are to be placed to form an operative arrangement. The system represented in the drawings includes a plurality of toll omces, each of which comprises a toll board with and cords for answering local manual and lcrlbers' lincsand from other toll omces and for calls' incoming from but is applicable generally to any voice operators positions dial omces, from toll sub- 45|. and con rol relays 453,

1 converting the impulses into voice frequency sig ized relay, l mally energized in the direction which effects 'closes its lower contact due to extending incoming calls to switching trunks leading to called manual and dial local omces, to intertoll trunks and to called toll subscribers lines. Outgoing jacks are connected to trunks to lecal omces. to toll subscribers toll trunks. Answering Jacks are directly connected to trunks from local offices, to toll subscribers lines, to intertoll trunks, and to incomtrunk circuits and with trunks to called toll and local oillces. The operators positions are provided with dials for use in controlling the operation of toll route selectors in other toll offices an'd for controlling the operation of selector and connector switches in local dial oillces.

lines and to interv: comprising resistors 46| and ing winding is effective to open the left contact and close the right contact of the relay in question. When the upper winding of relay 410 is energized, it overcomes the opposing energization of the biasing winding t0 open the left contact and close the right contact. The network 462 and condenser 463 associated with the upper winding of relay Reference may be had to the patent to R. E.

King et al., No. 2,209,777, granted July 30, 1940, for a detailed description of ythe cord and operators position circuits provided in each of the toll oilices for interconnecting calling and called lines and trunks and controlling the completion of toll calls. The `outgoing trunk circuits OTI, 0T2 and GT3, incoming trunk circuits ITI and IT2, the two-way trunk circuits TWTI, TWT2 and TWT3, and the toll route selector circuits TS2 and TS3 are -all similar 4to corresponding circuits in the aforementioned King et al. patent. The toll line circuits TLCI and TLC2 and the associated signal transmitting and receiving circuits STI, ST2, SRI and SR2 are arranged for voice frequency signaling over the associated toll line, whereas in the aforementioned King et al. patent composite signaling circuits are associated with the toll line. l

The toll line circuit TLCI comprises a repeating coil RCI, a directionally selective coil 400 `and a cut-oil' relay 490 for disconnecting the talking conductors 49| and 492 of the associated outgoing trunk circuit line TLI whensignals are being transmitted to or received from the second toll oillce. A repeater termination consisting of condenser 495 and resistor 496 is connected across the talking conductors of trunk circuit OTI while signals are being transmitted or received over the toll line. 'I'he toll line circuit TLC2 is similar to the line circuit TLCI, the reference characters of like elements having the same tens and units OTI from the toll digits. The toll line circuit TLCI may also be similar to the line circuit TLCI.

The signal transmitter STI comprises relays 44| and 442 which respond to direct current signais received over conductor |64 from the outgoing trunk circuit OTI on calls outgoing over toll line TL|2 and from two-way trunk circuit TWTI on calls incoming over toll line TLI2. The transmitter STI further comprises control relays 443, 444, 445, 446 and 441, a delay network closure of the upper contact.

the upper winding of which is nor- `Wnen relay m the energization of its` operating winding, the energization of the upper winding of relay 453 is reversed to 'effect closure of the left contact of this relay. The delay network 464 delays for about .050 second-the response of relay463 to' the operation and to closure of its right contact.

450, 455 and 410 for i similar to an answering 460 and the network comprising're'sistors 41| and 412 and condenser 413 associated with the upper winding of relay 410 render these relays slow in actuating their` contacts; so that opening of the left and closure of the right contacts of relay 460 occur about .025 second after the circuit for energizing the upper winding of relay 410 is opened and the opening of the right and closure of the 'left contacts of relay 460 occur about .050 second after the circuit for energizing the upper winding of relay 410 is closed. The

voice frequency signals are transmitted from sources GI, G2 and G3, through transformer 454, back contacts of cut-oil' relay 490, directional coil 400 and repeating coil RCI to the conductors of toll line 'I'L|2. The transmitter STI further comprises relays 480, 48| and 482 and interrupter 465 for effecting the transmission of a disconnect acknowledgment signal on incoming calls` 'Ihe delay network4 450 delays the response of signal control relay 453 to loperations of signal receiving relay 44| for about .050 second to allow time for the transmission of the enablement signal preceding dial impulse and similar signals. A seizure -signal sent by transmitter STI on an outgoing call consists of current of frequency fI from source GI for about .035 second followed by current of frequency f2 from source G2 for about .050 second. To transmit a train of dial impulses, a preparatory or enablement signal precedes the first dial impulse. the enablement signal consisting of current ofA frequency f2 for about .025 second followed by current of frequency fI for about .025 second. The enablement signal is immediately followed by current of frequency f3 for the duration of the dial impulse, current of frequency fi being transmitted at the end of each impulse of the train, except the last, until the next. impulse begins and at the en d of thelast impulse of the train for an interval of about .050 second. A ringing or a rering signal transmitted onan outgoing call is,

similar to a train of dial impulses consisting of a single impulse. An answerng supervisory or off-hook signal transmitted by the signal transmitter STI on an incoming call is similar to the aforementioned seizure signal. An on-hook supervisorysignal transmitted by the signal transmitter STI on an incoming call consists of the enablement signal followed by current of-trequency f3. An all-trunksabusy signal is supervisory signal followed by a succession of on -hock signals similar to dial impulse signals. A disconnect signal transmitted by signal transmitter STI on an outgoing call to effect releasev of the connection at thev distant end of toll line TL|2 consistsof the aforementioned enablement signal followed immediately by current of frequency f3 for about .150 second; and this entire disconnect signal is periodically repeated until a disconnect acknowledgment signal `is received by the associated signal receiver SRI. A disconnect acknowledgment signal transmitted by the signal transmitter STI on an incoming'call consists of current of frequency f2 for about .025 second followed by current of frequency f3 for about .025 second: and the` a1- ternatetransmission of impulses of current'ol these two frequencies continues until the discon- I40 are operated as described in the aforementioned patent o f R. E. King et al. The operation of relay |40 closes a circuit from battery through resistor |42 and conductor |64 for operating relays 44'I and 442 of the signal transmitter STI. The operation of relay 44| closes nect signal, incoming over the toll line TLI2 to the signal -receiver SRI, is terminated.

The signal transmitter ST2 is similar to the signal transmitter STI exceptthat it is arranged to transmit a different setI of three frequencies so as to prevent interference with signals being simultaneously transmitted in opposite directions over toll line ".IZ'LIZ. Corresponding elements of transmitters STI and ST2 are identified by reference characters having like tens and units digits.

The signal receiver. SRI comprises an' amplifier 40|, high-pass and band-pass filters 402 designed to nass only the signaling frequencies f4, f and f6 which are transmitted by the signal transmitter ST2. a volume limiting amplifier 403,

band-pass filters 404, 405 and 406, each designed to pass current of a different one of frequencies f4, f5.and 1,6. amplifier detectors 401, 408 and 409. relay 4I0 for responding to signaling current 'z of frequency f4, relay 420 for responding to sig- -naling current of frequency f5, and relay 430 for responding to signaling current of frequency J6. The signal receiver SRI further comprises relays 4I4, 4I5, 4I 6 and 424 for converting the incoming voice frequency signals into direct our? a circuit from battery through resistor 45| and the upper winding of relay 453 in parallel with resistor 452, thence through'the lower inductors of the delay network 450 to ground at the front contact Vof relay 44| The energizatlon of the upper windingl of relay 453 isdelayed by the network 450 for about fifty thousandths of a second, during which time a succession of relay operations are effected and an impulse of -current of frequency lIl is transmitted over line TLI2.

The operation of relay 442 closes a circuit for rent signals which are transmitted over conductor 1 to trunk circuits OTI, TWI'I and ITI. and

comprises a relav 435 which responds to an in coming disconnect acknowledgment signal to end the transmission of a disconnect signal. Relays 4I0, 420 and 430 are normally released polarized relays, each` of which has an operating winding and a biasing winding. Each of relays 4I4 and 424 is a. normally operated polarized relay, which has two operating windings and a biasing winding. Relay 4I5 is a normally released polarized relay having two operating windings and a biasing winding. The network comprising resistors 4II and 4I2 and condenser 4I3 and the network comprising lresistors 42| and 422 and condensery 423 are designed to make the associatedone of relays 4I4 and 424 slightly slow in releasing. when the circuit through its middle winding is opened and to delay its reoperationfor about .030 second when the circuit through this winding is again A closed. The network comprising resistor 4.48 and condenser 443 is designed to delay the response of relays 4|5 and 424 for about .030 second when the circuit through their lower windings is opened.

The signal receiver SR2 is similar to the signal receiver SRI except that it is designed to respond to signals consisting of impulses of current of frequencies f I, f2-and f3 instead of impulses of current of frequencies f4, f5' and f6. Corresponding elements of receivers SRI and SR2 are identilied by reference characters having the same tens and units digits Assume now that the toll line 'Y'IL`I2'isl idle and rthat an operator at the first toll oillce answers a call with plukAPI of cord CDI and then inserts the calling plug CPI of this cord'in jack J I of outgoing trunk circuit OTI. Relay |04 is operated by the connection of battery to the operating relay' 443. The cut-off relay 490 of toll line circuit TLCI is normally-energized in a circuit which is traced from battery through. the left contact of relay 4I5 of signal receiver SRI, winding of relay 430 and back contacts of relays 482, 444, 441 and 443 to ground; and this circuit' is opened by the aforementioned operation of re-Y lay 443 to cause the release of relay 430 and thereby open the talking connection between trunk circuit OTI and toll'line .'I'LI2. Relay 443 also opens the normallyclosed circuit for energizing the upper winding of relay 465, closes a circuit for operating relay 444, and .closes a circuit for starting `the transmission of current of Ifreduency ,f I lover toll line TLI2. The operation of relay 444 opens further the normally `closed circuit for energizingthe winding of the cut-off relay 490, prepares acircuit for the energization of the upper winding of relay 410, closes a circuit for operating relay 445,`prepares a circuit for the operating relay 464, and connects ground to conductor 463 in parallel with theconnecticn of ground'to this conductor` by the operation of vrelay 443. `The operation of relay 445 prepares circuits for operating relays 446 and 441 when the connection is released by the calling operator. The aforementioned circuit, which is closed by the operation of relay 443 to eiect the transmission of current yof frequency fl, is traced from generator GI. through the backV contact of relay 464', back.contact of.

relay 453, right windings of transformer 454; back contact of relay 465. to ground at the right front contact of relay 443.

current of frequency fi begins, relay 453 operates thereby vdisconnecting generator GI from the right windings oftransformer 454 and connecting lgenerator G2 to these windings. The impulse of current of frequency fl is thus terminated and an impulse of current of frequency f2 is initact of relay 4'|5`of signal receiver SRI, winding ofrelay 490,-back contact .of relay 482. right contact of relay 465 to ground at the right front contacts of relays 443 and 444. Thus a seizure signal has been transmitted through coil 400'andv repeating coil .RCI over toll line TLI2 tothe sleeve conductor of Jack .l I `and relays IIO and About fifty thousandths of a second after the operation of relay. 44.I and about .035 second after the impulse of second toll cnice, the signal consisting of current oi' frequency fl i'or about .035 second followed by current of frequency f2 for about .050 second to prepare the signal receiving equipment in the second toll oilice for selective dial impulses.

'I'he seizure signal thus transmitted by the signaltransmitter BT,| over toll line TL|2 is further transmitted through repeating coil RC2, directional signaling coil 500, ampliiier 50|. lters 502, volume limiting ampliiier 505 to the input side of band-pass lters 504, of current of frequency f| passes through lter 504 and is reotiiied by the amplifier detector 501 to eilect the operative energization of the lower winding of signal repeating relay 0. 'I'he volume limiting amplifier 503 limits the energy level in its output circuit suiiiciently to permit the energization of only one of signal receiving relays 5|0, 520 and 550 at a time thereby reducing the possibility of false operation in response to voice or noise currents. The operation of relay 5|0 5 |4 is again closed, the operative this winding being delayed for v about .030 second due to the discharge of condenser 4|3. The current of frequency f2 immediately following the current of frequency ll effects the operation of relay 520. The operation of relay 520 causes the deenergization of the middle winding of relay 524 to effect closure of the left contact of relay 524, only slightly delayed due to the charging`of condenser 525. 'I'he operation oi relay 520 also closes a circuit from ground through its left contact, left contact and lower winding winding of relay 5|5 and the winding of relay 5|5. Relay 5I. is operatively energized by the current in thiscircuit/and is locked under the control of relay 530.-v rThe energization of the lower winding of relay 5|5 effects the opening of its right contact to release the cut-oil' relay 590: and the closing ofthe left contact of relay 5|5 short-circuits the lower windi of relay 530.

. thereby to decrease the bias o! relay 530. The

' absckcon-taet yautres energization oi' the lower winding of relay 5 |4 maintains closure of the left contact of relay 5|4 i until relay 5|5 has operated and locked. The

operation of relay 5|5 short-circuits the lower windings of relays 5|5 and 5|4 and closes a circuit for operating relay 505 of two-way trunk circuit TWT2 as hereinafter described. When the lower windings oi' relays 5|4 and 5|5 are short-circuited by relay 5| 5, the aforementioned energiaation of the middle windingof relay 5'I4 effects the opening of the lett contacts of relay 5|4: but the sho ing oi' relay l|5 is lneiiective to restore the contacts of this relay to normal because the middle -winding of relay 5|5 is energized by current condenser |45 in through 'c a circuit traced from battery the middle winding of relay 5|5,

left contact contact oi' denser 545 of relay 524. throughanother back toground. 'Ihe chargingci'condenser the circuit through the middle o! relay 5|4, lower -circu'lting of the lower windof relay 541, lower winding and` 505 and 505. The impulse this closure being 4 j number in case the relay 541, resistance 545 and concurrent in this circuit tends to main- 75 tain the closure of the left contacts of relays 5| 5 and 524: but this is of no utility until dial impulse signals are being received as hereinatter described. When the current of frequency f2 ends, relay 520 releases thereby again closing the circuit i'or energizing the middle winding of relay 524: but the opening of the left contact ot relay 524 is delayed for about .030 second due to the discharge of condenser 523. When relay 5|5 restores its contacts to normal due to deenergization of its middle winding, the short-circuit across the lower winding of relay 530 is opened and the cut-oi! relay 550 is reoperated.

'Ihe aforementioned circuit for operating relay 505 o! two-way trunk circuit TWT2 is traced from ground through the right contact o! relay 550, the right front contact of relay 5 5, conductor 110, a back contact of relay 1|0 of outgoing trunk circuit OTI, conductor 159, back contacts ot relays 504 and- 501 of two-way trunk circuit TWT2, and through the Winding of relay 503 to battery. The operation of relay 503 connects ground to conductor 520 to mark the trunk TL|2 busy in the banks of selectors TSB and closes a circuit for operating relay 505 of trunk circuit TWT2 in series with the line relay 551 of the selector TS2. 'I'his circuit is traced from ground at the right contact of relay 530 through the right front contact of relay 5|5, conductor 110, back contact of relay 1|0, conductor 159, back contact oi' relay 504, winding of relay 505, a front contact of relay 503, conductor 151, thence in simplex through both windings of retard coil 150, conductors 15| and 152, back contacts of relay 190, conductors 50| and 502, front contacts of relay 505, conductors 55| and 552, back contacts of relay 550, resistors 55| and 552, to and through resistor 555, thence through a back contact of relay 550 and the winding oi' relay 551 to battery. The operation of relay 505 closes a relay 505 and a circuit for operating slow-torelease relay 501. Relay 501 closes a circuit for holding relay 505 and connects ground to conductor 553 to operate relay 580. Relay 580 disconnects the outer front contact of relay 545 from the winding of relay 545 to prevent the operation of relay 545 when a disconnect acknowledgment signal is transmitted as hereinafter described; closes a circuit i'or operating relay 58| of signal transmitter ST2; and disconnects ground from the contact of relay 58| to prevent the operation oi'- relay 552. 'Ihe aforementioned operation of line relay 551 of selector TS2 closes a circuit for operating slow-to-release relay 555. Relay 550 connects ground to conductor 553 and connects ground to conductor 559 leading to an alarm circuit to initiate a timing operation for eii'ecting an alarm in case the selective operation of selector TS2 is not completed within a predetermined vinterval of time. No further operations occur untilthe calling operator dials the iirst digit of the code of the called toll route or local exchange in which the called subscribers line terminates The calling operator in the ilrst toll oiiice now dials the toll route code and also the local oiiice code oi' numerical digits of the called subscribers call is for a subscriber in an' automatic local omce, relay being alternately released and reoperated in response to each dial impulse thus created. Each release and reoperation o! relay eii'ects a corresponding release and reoperation of relays 44| and 442 of the signal transmitter STI. The release c! relay 44| eiiects the reversal of current through the upper winding of relay 455 to cause the release of circuit for holding l Ysecond after the may 45a abaut' .o so second after-,remy rre leases. The release'of'relay 442 causes the release of relay 443 and the energization of the upper winding of relay 4|||, thereby effecting the opening of the leftcontact of relay 410. The re mission of an impulse of current o f frequency f2 over toll-line TL|2 is thereby initiated. Since relay 444 is slow in releasing, it remains operated during the transmission of dial impulses. The aforementioned opening of the left contact of relay 410 causes Vthe deenergization of the upper winding of relay 450 to effect the opening of the left contact and closing of the right, contact of relay 460, thereby to end the current of frequency f2 and initiate the transmission .of current of frequency Il over line TL|2.. Due t the delay eilect of the resistor condenser networks associated with'relays 415 and 4451|, the opening of the left contact and the closure of the'right contact of relay 450 resulting from the opening of the left contact of relay 410 occur about .025 second afterthe closure of the left contacts of relay 455; so that the impulse of current of frequency f2 endures for about .025 second. When relay 453 releases about .050 second after the release of relay 44|, it disconnects generator GI fromI the right windings of transformer 454 and conf,

nects generator G3 to these windings,A thereby ending the impulse of`- current of frequencyv fl and initiating the transmission of current of frequency f3 over lineTL |2, the current of frequency f3 representing the dial impu which has effected the release of relays44| and 442.

The current of frequency 13 continues until relay V 453 again operates due to the reoperation of relay `44| at the end of the dial impulse. When relay .453 reoperate's, ytlie t :nu on of'curre'nt of frequency. Il'endsfand the on of current of frequency. llis resumed. Each release and reoperation of" relay 453, under the control of relay 44| in responseto succeeding impulses of the train created by, thedia'ling of the first digit,

41| to effect the closing-of the left contact of relay 415; and the closing of the left contact of relay 410 causes the `reenergization of the upper winding of relay 450 to effect the opening of the 1 rightc'ontact-and closure of the' left contact of relay 455. The opening of the left contact and closure of the right contact of relay 455 is effective to. open the circuit through the right windings of transformer 454 and to -reoperate the impulse followed by current of frequency] I during the interval between impulses and following the last impulseof-the train. The .dialing of each additional digit by the calling operator effects.

the transmission of the enablement signal and a train-of dial impulses over toll. line TL|2 in the above-described manner. When dialing is completed, the release of the dial key (not shown) effects the operation of relay in in the `manner described in the aforementioned Kinget al. .pat-

ent, thereby to close the talking connection beeffects the transmission of ,an impulse of current l Iof frequency followed by an impulse of current of frequency Il. Since relay-454 is slow to' release.- it remainsoperated during the transthe response ofrela'yyltpr the closure of the mission of a train of dial impulse signals: since f circuit through itsupperwinding' .is delayed .by

the associated resistor'condensernetwork. the

closure "of the left contact of relayl' is maintained .during `their onof the train of dial impulse signals;"and since thenoperative ref spense ofeach of relaysg4'l4 and-455m delayed by 'the' associated resistor condenserfnetwork,

. lle. lay 46|k does not open its rightcontact d reoperation-cfrelay 4143 at: the end ci the last. immune of the m opens its left contact of current of the. on of aftrain ofdiai After receiving the of a train, relays v 44|, ,442 and 443, operated. About :100`

v and closes its right contact thereby endins- .the an. frequency-1l- The Aor relay m causes the .deenergiz'ttion of the me:

tween cord CDI and toll line TLI2.

The signal receiver SR2 receives the enablement signal and train `of dial' impulses correspending to each digit dialed, the first digit being effective Vto selectively -operate the selector TS2 to select a group of trunks corresponding to this digit. Relays 525 and 5H! are successively operated by the enablement signal and relays 53u and 5in are thereafter successively operated responsive to each dial impulse signal. The operation of relay 52|), in response to current of frequency f2. opens the circuit through the middle winding of relay 524 to effect the closing of theleft'contact of relay 524, the delay network comprising resistors 52|v and 522 and condenser 523 being effective to maintain closure of this contact for about .030 second after relay 525 releases at the end of the impulse of current of frequency f2. I'he opera-tion of relay 5in in response to the current of frequency 1| causes the deenergization of the middle winding of relay 5|4 to effect -clnsure of the left contact of relay 5i4 and closes a circuit through the left contact and lower winding of relay 524, a back contact of relay 541 and middle winding of relay 5|5. The energization of the lower winding ofrelay4 524. bythe current in this circuit, maintains closure of the left contact of relay 524; and the energization of the middle winding of relay 5|5 effects the opening of the right contact of relay 5|5, to release the cut-off relay 550, and eifects the closing of the left .contact of relay 5l5 to' short-circuit the lower winding of relay 534 and thereby reduce the bias of relay 535 to renderit responsive to dialr impulses. The delay network, comprising resistors/5Hv and 5|2 and condenser 5|3', maintains closure of the left. contact of relay 514 after relay 5|! releases at the end of the 'current `of frequency vli.v The operation of relay 535 in ref spouse to the currentof frequency f3, represent-f fing the open period of the first dial limpulse cycle,

closes a circuit for discharging condenser 545 and closes a circuit for energizing the lower winding of relay v524 in series' with the middle winding of relay 5|5 so-adto maintain the closure of the i left contact of relay 524 ,and .to maintain closure ofprelay 7s of the left contact of IIL The operation ,sponse to alternate currents train corresponding to of relay 536 opens the holding circuit of relay |6 and disconnects ground from conductor 116 thereby to repeat the dial impulse to relay 665 of two-Way trunk circuit TWT2 and line relay 651 of selector TS2. When relay 536 releases at the end of the impulse of current oi' frequencyjt, the holding circuit for relay 5|6 is again closed and ground is reconnected to conductor 116. Being slow in releasing, relay 5|6 remains operated during the response of relay 536 -to dial impulse signals. After relay 536 releases, the closure of the left contact of relay 524 is maintained by current through the lower winding of relay 524 charging condenser 549, this current also being effective to maintain the energization of the middle winding of relay 5I5 and thereby maintain closure of the left contact of relay 5|5. When relay 5|6 is reoperated by the current of frequency fl representing reclosure of the dialing circuit, the circuit through the middle winding of relay 5|4 is-opened so as to maintain the closure of the left contact of relay 5|4. Succeeding alternate operations of relays 530 and 5|6, in reof frequencies ,f3 and maintain the closure of the left contacts of relays 5|4, 5|5 and 524 and effects the alternate disconnection and reconnectionl of vground to conductor 116. About .030 second-after relay 5I6 releases, at the end of the impulse of current of frequency fl .representing closure of the dialing circuit following the last impulse of the train, the contacts of relays 5|4, 5 I 5 and 524 are restored to normal and the cut-olf relay 596 is reoperated.

When relay 536 of signal receiver SR2 disconnects ground from and reconnects ground to conductor 116 in response to each dial impulse of the nrst digit dialed by the calling operator,

relays 665 and 651 are alternately released and' reoperated a corresponding number; of times. Being slow in releasing, relays 661 and 656 remain operated during the response of relays 665 and 651 to dial impulses. The release of relay 651 in response to the first dial impulse closes a circuit for operating the vertical stepping magnet 661 and relay 669 in series. This circuit is traced from battery through the winding of stepping magnet 661, winding of relay 666, a front contact of relay 658, back contact of relay 651 to ground at a back contact of relay 666. magnet 661 steps the brushes 61|, 612, 616 and 614 up to the rst level of the terminal bank, the vertical off-normal springs 664 being actuated as soon as the shaft on which the brushes are mounted moves out oi normal'posltion. A The operation of relay 666 and actuation of springs 664 close a circuit for operating relay 665. Relay 665 locks in a circuit traced from its winding through thelower contact of springs 564, back contact of rotary contact of` relay 665, to ground at a back contact of relay 666. When relay 651 reoperates at the end of the rst dial impulse, the stepping magnet 661 releases. Being,s1ov`r in releasing, relay 666 remains operated until all of the impulses in the been received. Each succeeding releasevand reoperation of relay 651 causes a corresponding peration and release of stepping magnet 661, the brushes of selector TS2 being thereby stepped up to th level corresponding to the digit dialed. When relay 666 releases following the reoperation of relay 651 at the end of the last impulse ot the train, it closesxa circuit for operating the rotary stepping magnet 666. this circuit beingv traced from the winding oistepping magnet 666,

The operation of stepping` the flrst digit dialed have .stepping magnet 666.

lower front contact ot relay 666, and back contact of relay 666 to grounded conductor 653. The operation of stepping magnet 666 steps the brushes into engagement with the ilrst set of terminals in the selected level, 'Ihe operation of stepping magnet 666 causes the release of relay 665; .and the release of relay 665 causes the vrelease of The release of stepping magnet 666 closes a test path from battery through the winding of relay 665, lower contact of springs 664, back contact of stepping magnet 666, a back contact oi' relay 666, and test brush 613 to the terminal engaged thereby. If the ilrst set of terminals is connected to a busy trunk or selector circuit, the terminal engaged by test brush 613 is marked by the connection of ground potential thereto; in which case, relay 665 is reoperated to again close the circuit for operating stepping magnet 666. The brushes are thereby advanced to the next set of terminals, the test circuit being again closed when stepping magnet 666 releases. The brushes are in this manner advanced step by step in the selected level until they engage a set of terminals, the test terminal stepping magnet 666, upper y of which is not marked with ground potential connected thereto. Whereupon relay 666 is operated by the current in a circuit from battery through the winding of relay 565, lower contact of springs 664, back contact of stepping magnet 666, winding of relay 666, lower back contact of the 11th rotary step springs 656, to grounded conductor 653. Being marginal, relay 665 is not operatively energized in series with the winding of relay 666. The operation ot relay 666 disconnects the winding of line relay 651 from conductors and 662 and connects these conductors through its front contacts and brushes 61| and 612 to the conductors of the selected trunk which may be connected to an incoming trunk circuit such as IT2, to an auxiliary selector, to a switch-y ing trunk to a local manual or dial oiiice, or to a trunk to anothertoll oiilce, depending upon lthe particular call which is in question. Relay 651 releases, when it is disconnected from conductors 65| and 652, causing the release of relay 656. Relay 658 disconnects ground from conductor 656 to stop the alarm circuit operation and disconnects ground from conductor 656, this conductor continuing, however, to be connected to ground at the lower iront contact of relay 661 of two-5 way trunk circuit TWT2.

Assume now that the call is one which is routed to a toll operator in the second toll oiilce for completion through a cord at the answering toll operators position. In this case, the selected set of terminals 616 are connected to an incoming trunk circuit ITZ. Reference may be had to the aforementioned patent to King et al. for a complete disclosure of the incoming trunk circuit ITI. Upon selection oi' this trunk circuit, the line relay |665 is operated in series with relay 665 of twoway trunk circuit TWTZ in a circuit traced from s ground at the right contact of relay 566. right the winding of linerelay` |666 to battery. Relay |666 cloeea a circuit for lighting the answering lamp LI to signal an operator. When the'call is answered by the insertion of the answering plug AP2 of a cord CD2 in jack JIU, relay |034Jis operated in'the manner described in the aforementioned Kinget aLpatent, thereby connecting ground to conductor I|I|l4,` through the lowest terminal of set 515, brush 614, a front contact of relay 555, upper back contact of springs 555,.con ductor 554, and through the winding of relayll'l of two-way-trunk circuit TWT2 tobattery. Relay 5|| operates', closing'a circuit from battery through the front contact oi' relay 5| I, right contact of relay 5 I 5, conductor 155, left contact of relay 145, conductor 154, back contact of relay 545 of signal transmitter ST2, and windings of relays 54| 1 and 542 to ground. The operation of relay 54| effects the reversal of current through the upper winding of relay 553 thereby to Veffect the-opera tion of relay 553, the operation of relay 553 being delayed for about .050 second by the delay network of relayv 543 being delayed for about '.050 secondV 555. The operation of relay 542 causes the operation of relay 543. The operation of relay 543.v causesthe operation of relay 544 and the release of cut-of! relay 595, and connects ground to conductor 583 to start the transmission of current of frequency f4 through transformer 554, directional coil 555 and repeating coil RC2 over toll line -TLI2 ,Y

to the flrst toll office.

through the upper winding of relay 555, the .opening of the right contact and closing of the left contact of relay 555 being delayed for about .100

vsecond by currentcharging condenser 555.. The

operation of relay 544 connects ground to conductor 553, holds openthe circuit through the winding of cut-orf relay 530 and closes a circuit for operating relay 545. The operation of relay 545 prepares a circuit for operating relay 541 The operation of relay 553, about' .050 second after' the operation of relay 54|, ends the transmission of current of frequency f4 and initiates the transmission of current of frequency f5. When relay 555 opens its right contact, it ends the transmission of current of frequency ',5 and closes Va circuit for reoperating the cuto relay v555. vThus an answering supervisory or off-hook signal is transmitted by the signal transmitter ST2 over The operation of relay .Y 543 also opens the normally closed circuit of relay 54I- causes a yreversal leof the energization of ythe upper winding of relay 543, the response opening of the left contact of this relay to. release cut-oif relay 535 and theclosing of the right contact to start the transmission of current of frequency f5 over line TLI2. The opening of the right contact of relay 515 causes the deenerglzation of the upper winding of relay 555 to effect the opening of the right contact a'nd closure of..

the leftcontactof' this relay, whereby the trans mission ofcurrent of frequency f5 is ended and the transmission of current of frequency f4 started. When relay'553 releases, the transmission of current of Vfrequency f4 is ended and the transmissionof current of frequency l5 started. If the on-hook condition continues to exist until relay 544 releases, the release of relay 544 dis- .fconnects vground from conductor 553 thus ending the transmission of current of frequency f5. The release of relay544 also effects the reoperation of relay '595, the operation of relay 541, the release of relay 545 and the deenergization of the upper winding of relay 515, thereby to leffect the closing of the rightI contact of relay 515. The

closing of the right contact of relay 515 effects the reenergization ofthe upper winding of relay ssn ,thereby to cause the opening of the right contact and closureof the left contact of relay 555. The release of relay 545 causes the release of relay 541. The on-hooksignal thus sent from transmitter ST2 lover line TL|2 operates signal receiver SRI in similar manner to that in .which the signal receiver SR2 operates in response to a v single dial impulse except that,`since the current line TL|2 in response to the answering of the call v by an operator in the second `toll cnice. After' 5 the transmission of this signal, relays 54|, 542,v 543, 544, 545, 555 and 58| remainoperated, relay' 553 maintains closure'of its right contact, 'relay 555 maintains closure of its right'contact, relay' 555 maintainsA closure of its left contact,.and relay 515.maintains closure of its right contact.

The answeringfysupervisory signal thus trans-- Y mitted from signal transmitter' ST2 over line TLI 2 operates signal receiver SRI, in similar manner to that in which the signal receivi SR2 is oper-V atedj responsive to a seizure signalhereinbefore described, to connect ground to conductor |15 to cause the operation offsup'ervisory relay |55."A The operatign of the'caiung operato' relay im or incoming circuit IT2 releases, in turn causing the release of Irelay 5|| of two-way trimkl circuit The relea'seof relay 5|| Icauses the release-o! relays 54| and 542 thereby `to effect the transmis'- sion of an enabiement signal, eonsuung'or 'current of frequency f5 followed b'ycurrent of frequency f4, followed by an on-hook signal consisting of y eurrentXof.A frequency f5. The release relay msopens tnecireuit through? the lower, low-resistance winding of relay .|541toextinguish the calling cord supervisorydampjALl'.- If the answering'operator disconnects before# of frequency f5 continues for relay 435 is operated long en glrto cause the utgrsoseeond,

release of relay 4|5 and thereby disconnect ground vfrom conductor |15.. Thief-(disconnection offv 5d ground from conductor |15 of relay ne mum the canins cord' supervisory lamp ALI. If the answering. operator again incalling operator disconnectsQanoff-hook 'signal isagaintransmittedtothecallingoperatorinthe -4 manner hereinbefore described. iii

' serts the plug of a cord in jack'll beforethe y .un the ceiling operator wisnesmrecan triey v answering operator, the operation ofthe key (not shown) effects the momentary release ofreIay |45, thereby effecting the momentary ro;v

lease of relays 44| and 442; whereby animal isI transmitted ,over toll line TLI2, Vwhichiignalis"- the same as that for a trainof dial impulses consisting of aslngle impulse.v In response"to this' Signal; the signal receiver SRI Imomltarily disconnects groundjfrom conductor 11|',causing the release and'reoperation of ,relay |3550! inf coming trunk circuit :The'responaeof relay to 4the,'answering .operator infthe" manner d|s.

lm causes'anningrecauagnnmjbe given closed 4in the aforementioned King etal. patent..V

When tliecallin'gl operator releases 4the connection by withdrawing 'plug CPI from-jack Jl'lh er relaysmflll, im me uns n operated, relay 'lll'also releases. The-"release of |45 causes the successive release of re-' over line TLI 2,

' successive operation of relays lays 44|, 442, 443 and 444, thereby eecting the transmission of the enablement signal in the manner hereinbefore described. When relay 453 releases, responsive to the-release of relay 44|, it ends the transmission of current oi' frequency ji and initiates the transmission of current of frequency f3. The release of relay 444 causes the operation of relays 446 and 441. Relay 445 is suillciently slow in releasing so that operated while the disconnect signal is being transmitted. The operation of relay 441 prevents the reoperation of the cut-oil' relay 480, short-circuits the lower winding of relay 430 of signal receiver SRI to renderrelay 430 operative in response to current of frequency f incoming and connects the winding of relay 435 of the signal receiver in series with the locking'winding of relay 424 in preparation for response to a disconnect acknowledgment signal incoming over line TLI2 from the second toll omce. The operation of relay 448 closes a circuit for reoperating relays 44| and 442 thereby causing the successive reoperation of relays 443 and 444 and the delayed operation of relay 453. The reoperation of relay 444 causes the release of relays 446 and 441. The release of relay 446 causes the successive release of relays 44|, 442, 443 and 444 and the delayed release of relay 453. Thus relays 44|, 442, 443, 444 and 453 are released and reoperated and relays 448 and 441 are operated and released in a repeated cycle until a disconnect acknowledgment signal is received by the signal receiver SRI. The interval of time during which relay. 443 is operated during each cycle of these disconnect signal operations, is not long enough to cause the opening of the left contact of relay 465 and the interval of time during which relay 444 is released or relay 443 operated is not long enough to cause the release of relay 484; so that the current of frequency f3 continues until relay 453 reoperates in response to the reoperation of relay 44|. While the interval of time during which relay 442 is released and relay 444 is operated is long enough to eiect the 410 and 460, these relays are againreleased due to the next sucit remains impulse of current of frequency f2, of the disconnect signal does operation of relay v5|5.

When ground is disconnected from conductor 110, due to the operation of relay 530 and release of relay 5I6, relay 605 of ytwo-way trunk circuit TWT2 and relay I 005 of incoming trunk circuit IT2 release. The continued release of relay 555 causes the successive release of relays 801 and 503. A disconnect signal is given to the answering operator and the return to normal of trunk circuit ITZ is effected in the manner described in the above-mentioned patent to King et al. The release of relay 801 disconnects ground from conductor 653 thereby causing the release of relay 668 of selector TS2 and the release of relay 588 of signal transmitter ST2. The release of relay 660 effects the return of selector TS2 to normal in the usual and well-known manner. The release of relay 585 opens the circuit through the the repeating not eifect the rewinding of slow-to-release relay 58|, vand causes ceeding reoperation of relay '442, before the reoperation of relay 453 occurs; tion of relay 453 is thus effective to end the current of frequency .f3 and to initiate the transmission of current of frequency f2. The reoperation of relays 410 and 485 resulting from each release of relay 442 ends each impulse of current ol' frequency f2 and initiates an impulse of current of frequency fi; and each impulse of current of frequency f I is ended when relay 453 releases. Thus the disconnect signal cycle continues until a disconnect acknowledgment signal is received by the signal receiver SRI as hereinafter described. v i

When the enablement portion of a disconnect signal, transmitted by signal transmitter STI, reaches the signal receiver SR2, relays 520 and 5I0 are operated in succession thereby eiecting the operation of relays 524, 5I4, 5I5 and 5I6 in the manner hereinbefore described. The current of frequency f3 following the enablement signal operates vrelay- 530, thereby to disconnect ground from conductor 110 and to hold relays 5I5 and 524. Since` the impulse of current of frequency f4 continues for about .150 second, relay 538 remains operated long enough to cause the relay 5I5. Since the reoperation oi' reeii'ected only by receiving an impulse of current of frequency fl followed by an lay 435. Relay 435 is ceiver SRI operate as above signal transmitter STI and 'oillce, the selector TSI the operation of relay 582 until relay 58| releases. The operation of relay 582 causesthe release of cut-off relay 580, closes a circuit for operating relay 564, connects ground to conductor 583 and connects the lower winding of relay 553 to the brush of interrupter 583. Relay 553 is thereby alternately operated and released under the control of interrupter 583, impulses of current of frequencies f5 and f5 being alternately transmitted over line TLI2 under the control of relay 553 as long as relay 582 is operated, When relay 582 releases, relay 553 remains normal, relay 564 releases, and cut-off relay 590 reoperates.

When the disconnect acknowledgment signal is received by the signal receiver SRI, relay 428I responds to each impulse of current of frequency f5 and relay 430 responds to each impulse of current of frequency f6. The operation of relay 428 causes the operation of relay 424; and the operation of relay 430 immediately following the operation of relays 420 and 424 closes acircuit from ground through the right contact of relay 430, right contact and lower winding of relay 424, inner front contact of relay 441 and winding of rethereby operated to end the cyclic operation of relay 446 and thereby prevent the reoperation of relays 44|, 442, 443, 444 and 453. Relay 464 now releases to end the transmission of current from any of sources GI, G2 and G8 and the cut-oir relay 490 is reoperated.

If the selector TS2 encounters an all-trunksbusy condition or busy dial signals arealtemately transmitted over the tolll line TLI 2 in the manner hereinbefore described.

On calls outgoing from the second toll office over toll line TLI2, the signal transmitter ST2 and signal receiverSRZ operate in similar manner to that in which the transmitter STI and redescribed, and the signal receiver SRI to that in which the and receiver SR2 operate as operate in similar manner transmitter ST2 above described.

On a call from the rst toll oillce to a third toll in the second toll office is selectively operated responsive to the first toll route digit to select' a set of terminals 615 con'- nected to the trunk and line circuits TWT3 and 'I'LC3 associated Awith an intertoll trunk line TL28 'leading to the third toll omce. If the toll line TL!! is arranged for voice frequency a signal transmitter to STI and signal receiver similar to the receiver SRI are associated with the line circuit TLC3 and a seizure signal is transmitted by the signal transmitter ST3 over line 'I'L23 to the third toll ofllce responsive to seizure of terminals 615. After the seizure signal has been transmitted over toll line TL23, selective and supervisory signals incoming over line TLI2 from the first office are repeated by signal receiver SR2 to the signal transmitter ST3 associated with toll line TL23 and are transmitted thereover in similar Y manner to that in which these signals are transmitted by the transmitter STI in the first toll oftlce. Since the cut-off relay 590 of line circuit TLC2 is operated at the time the irst part of any incoming signal is received by signal receiver SR2, a part of the signal isj transmitted through to toll line TL23 and thereover to the third toll oilice before relay 59u releases. The use of a two impulse enablement signal preceding selective and supervisory signals minimizes the probability of false or premature signal operations in the third toll office due to the transmission of part of a voice frequency signal, incoming over toll line TL23 to signal receiver SR2 before relay 590 releases. False signal operations are thus prevented in built-up connections without providing means for delaying the response to signals for an interval long enough to prevent a signal operation by that portion of a signal which is transmitted before the cut-off relay opens the talking connec-` tion at the intermediate switching point. Although it is not possible to introduce sufllcient delay to prevent such false operations when selective impulses are being transmitted by a highspeed dial, the use of a two-frequency enablement signal is effective to prevent false operations in built-up connections without limiting the selective impulse rate. I'he further operations of the signal transmitter STBand signal receiver SR3 are similar to corresponding operations of the signal transmitters STI and ST2 and signal recelvers SRI and SR2 as hereinbefore described.

What is claimed is:

l. In a signaling system, a plurality of sources of current, each source of a different frequency, a line, and signal transmitting means associated with said line, said signal transmitting means comprismg signal relays responsive to signals to be transmitted over said line, means responsive to the operation of said signal relaysfor transmitcomprising signal relays responsive to signals to be transmitted over said line, means responsive to the operation of said signal relays for transmitting a signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency, means responsive to the release of said signal relays for transmitting an enablement signal consisting of an impulse of current of said second frequency followed immediately by an impulse of current oi said first frequency and for transmitting current of a'third frequency immediately following the enablement signals, means responsive to the reoperation of said signal relays within a predetermined interval of time after their release for ending the current of said third frequency and for transmitting an impulse of current of said first frequency immediately following the current of said third frequency, means effective in case said signal relays are not reoperated within said predetermined interval of time for ending the current of `said third frequency. and a delay network effective to delay the transmission of impulses of current of said third and first frequencies corresponding to the release andthe reoperation of said signal relays for an interval equal to the interval required for the transmission of said enablement signal preceding the irnpulse of current of said third frequency.

3. In a signaling system, a plurality of sources of current, each source of a different frequency, a line, and signal transmitting means associated with said line, said signal transmitting means comprising signal relays responsive to a train of dial impulses to be transmitted over said line, means including relays controlled by the release of one of said signal relays for effecting the transmission over said line of an enablement signal consisting of an impulse of current of a rst frequency immediately following an impulse of current of. a second frequency, a relay operatively responsive to each release and each reoperation of another of said signal relays, the y release of the last-mentioned relay being effective to end the transmission of current of said first frequency and cause the transmission of an ting a signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency, meansk responsive to the release of said signal relays for transmitting an enablement signal consisting of an impulse of current of said second frequency followed immediately'by an impulse of current of said first frequency and for transmitting current of a third frequency immediately following the enablementsignal. means responsive to the reoperation of said signal relays within a predetermined interval of time after their release for ending the current of said third vfrequency and for transmitting an impulse of current of said rst frequency immediately following the current of said third frequency, and means effective in case said signal relays are not reoperated within -said predetermined interval of time for'ending the current of said third frequency. 2. In a signaling system, aplurality of sources of current, each source of a different fre'quency,

a line, and signal transmitting means associated with said line, said signal transmitting means impulse ofcurrent of a third frequency and the reoperation of said last-mentioned relay being effective to end the transmission of current of said third frequency and initiate the transmission of current of said first frequency.

4. In a signaling system, a plurality of sources of current, each source of a different frequency, a line, and signal transmitting means associated with. said line, said signal transmitting means comprising signal relays responsive to a train of dial impulses to be transmitted over said line, means including relays controlled by the release of one of said signal relays for effecting the transmission overv said line of an enablement signal consisting of an impulse of current of a rst frequency immediately following an impulse of current of a second frequency, a relay operareceive signals from said signal transmitting means, said signal receiving means comprising a rst relay means for responding to impulses of current of said third and first frequencies representing dial impulses, and comprising relay means operatively responsive to said enablement signal for rendering said first relay means operatively responsive to the impulses of current representing dial impulses.

6. In a signaling system according to claim 4, signal receiving means connected to said line to receive signals from said signal transmitting means, said signal receiving means comprising a first relay means for responding to impulses of current of said third and first frequencies representing dial impulses, and comprising relay means operatively responsive to said enablement signal for rendering said first relay means operativeiy responsive to the impulses of current representing dial impulses.

7. In a signaling system, a plurality of sources of current, each source of a dierent frequency. a line, and signal transmitting means associated with said line, said signal transmitting means comprising relay means for transmitting a signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency. relay means for transmitting trains of signals, each train consisting of any desired number of signals and each signal consisting of current of an impulse of current of a third frequency followed immediately by an impulse of current of said first frequency,

relay means for transmitting an enablement signal preceding each said train of signals,` said enablement signal consisting of an impulse of current of said second frequency'followed immediately by an impulse of current of said first frequency. and relay means for transmitting a signal consisting of said enablement signal followed immediately by an impulse of current of said third frequency.

8. In a signaling system, signal receiving means comprising relay means operatively responsive t0 a signal consisting of an impulse of current of a rst frequency followed within a predetermined interval of time by an impulse of current of a second frequency, relay means operatively responsive to trains of signals, each train consisting of any desired number of signals and each 'signal consisting of an impulse of current of a third frequency followed within a predetermined interval of time by an impulse of current of said first frequency, relay means operatively responsive to an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse of current of said second frequency followedv within a, predetermined interval of time by an impulse of current of said first frequency, and relay means operatively responsive to a signal consisting of said enablement signal followed by an impulse of current of said third frequency.

9. In a signaling system according to-claim 7, signal receiving means connected to said line to receive signals from said signal transmitting means, said signal receiving means comprising relay means operatively responsive to a signal consisting of an impulse of current of said first frequency followed within a predetermined interval of time by an impulse of current of said second frequency,` relay means rendered operative by said enablement signal for responding to said signals corresponding to a train of any desired number of signals, and relay means rendered 0perative by said enablement signal for operatively responding to an impulse of currentof said third frequency.

10. In a signaling system, a plurality of sources of current, each source of a di'erent frequency, a line, and signal transmitting means associated with said line, said signal transmitting means comprising rela'.' means for transmitting a signal consisting of an impulse of current of a first fre-l quency followed immediately by an impulse of current of a second frequency, relay means for transmitting trains of signals, each train consisting of any desired number of signals and each signal consisting of an impulse of current of a third frequency followed immediately by an impulse of current of said first frequency, relay means for transmitting an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse of current h of said second frequency followed immediately by an impulse of current of said first frequency, relay means for transmitting a signal consisting of said enablement signal followed immediately by an impulse of current of Isaid third frequency, and relay means for transmitting a signal consisting of an impulse of current of said second frequency followed immediately by an impulse of current of said third frequency.

ll. In a signaling system, signal receiving means comprising relay means operatively responsive to a signal consisting of an impulse of current of a first frequency followed within a pre- 40 determined interval of time by an impulse of current of a second frequency, relay means operative responsive to trains of signals. each train consisting of any desired number of signals and each signal consisting of an impulse of current of a third frequency followed within a predetermined interval of time by an impulse of current of said first frequency, relay means operatively responsive to an enablement signal preceding each said train of signals, saidenabling signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said first frequency, relay means operatively responsive toa signal consisting of said enablement signal followed by an impulse of current of said third frequency, and relay means operatively responsive to a signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said third frequency.

l2. In a signaling systemaccording to claim l0, signal receiving means connected to said line to receive signals from said signal transmitting means, said signal receiving means comprismg relay means operatively responsive to a signal consisting of an. impulse of current of said first frequency followed within a predetermined interval of time by an impulse of current of said second frequency, relay means rendered operative by said enablement signal for responding to said signals corresponding to a train of any ,desired number of signals, relay means rendered operative by said enablement signal for operatively responding toan impulse of current of said third frequency, and relay means operatively responsive to a signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said third frequency.

13. In a signaling system, a plurality of sources of current, each of a different frequency, a line, signal transmitting and signal receiving means at each end of said line for signaling over said line. the signal transmitting means at one end of said line comprising relay means for transmitting a signalv consisting of an impulse of current of a first frequency followed immediately by an impulse` of current of a second frequency, relay means for transmitting trains of signals, each train consisting of any desired number of signals and each signal consisting of an impulse of current of a third frequency followed immediately by an impulse oi' current of said first frequency, relay means for transmitting an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse of current of said second frequency followed immediately by an impulse of current of said first frequency. and relay means for transmitting a signal consisting of said enablement signal followed imt mediately by an impulse of current of sa'd third frequency. the signal transmitting means at the other end of said line comprising relay means for transmitting a signal consisting of an impulse of current of a fourth frequency followed immediately by an impulse of current of a fifth frequency, relay means for transmitting -trains of signals, each train consisting of any desired number of signals and each signal consisting7 of an impulse of current of a sixth frequency followed immediately by an impulse of current of said fourth frequency, relay means for transmitting an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse bf current of said fifth frequency followed immediately by an impulse of current of said fourth frequency, and relay means for transmitting a signal consisting of said enablement signal followed immediately by an impulse of current of said sixth frequency. the signal receiving means at said one end of the line comprising relay means operatively responsive to a signal consisting of an impulse of current of said fourth frequency followed within a predetermined interval of time by an impulse of current of said fifth frequency relay means operatively responsive to traim of signals, each train consisting of any desired num.- ber of signals ,andeach signal consisting of an irnpulse of current of said sxth frequency followed within a predetermined interval of time by an impulse of current of said fourth frequency rela" means operatively responsive to an'enablement signal preceding each said train of signals. said enabling signal consisting of an impulse of current of said fifth frequency followed within a nredetermined interval of time by an impulse of current of said fourth frequency. and relay means voperatively responsive to a signal consisting of l said enablement signal followed by an impulse of current of sad sixth. frequency and the ni'uial receiving means at saidotherfend of the line com- Drising relay means operatively responsive tn p.

:signal consisfinv of an impulse of cui-rmt of said first frequency followed within a nr^dtermined interval of time by an impulse of current of said second frequency. relay \means operatively responsive to trains of signals. each train consisting of any desired number of signals and .each signal consisting of an impulse of current of said third frequency followed within a predetermined interval of time by an impulse of current of said first frequency, relay means operatively responsive to an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said first frequency, and relay means operatively responsive to a signal consisting of said enablement signal followed by an impulse of vcurrent of said third frequency.

y14. In a signaling system, a plurality of sources of current, each of a different frequency, a line, signal transmitting and signal receiving means at each end of said line for signaling over said line, the signal transmitting means at one end 'of said line comprising relay means for transmitting a signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency, relay means for transmitting trains of signals. each train consisting of any desired number of signals and each signal consisting of current of an impulse of current of a third frequency followed immediately by an impulse of current of said first frequency. relay means for transmitting an enablement signal preceding each said train of signals. said enablement signal consisting of an impulse of current of said second frequency followed immediately by an impulse of current of said first frequency, relay means for transmitting a signal consisting of said enablement signal followed immediately by an impulse of current of said third frequency, and relay means for transmitting a signal consisting of an impulse of current of said second frequency followed immediately by an impulse of current of said third frequency, the signal transmitting means at the other end of said line comprising relay means for transmitting a signal consisting of an impulse of current of a fourth frequency followed immediately by an impulse of current of a fifth frenuency. relay means for transmitting trains of signals.v each train consisting of any desired number of signals and each signal consisting of current of an impulse of current of a sixth frequency followed immediately by an impulse of current 0f said fourth frequency. relay means for transmittine an enablement signal preceding each said train of signals. said enabl'ement signal consisting of an impulse of current of said fifth fre-A quency followed immediately by an impulse of current of said fourth frequency, relay means for transmitting a signal consisting of said enablement signal followed immediately by an impulse of current of said sixth frequency. and relay means for transmitting a signal consisting of an impulse of current of said fifth frequency followed immediately by an impulse of current 0`f said sixth frequency. the signal receiving means at said one end of the line comprising relay' means operatively responsive to a signal consisting of an impulse of current of saidfourth freouency followed within a predetermined interval of time by an impulse of current of said fifth freouencv, relay means operatively responsive to trains of signals, each train consisting ofV any desired number of signals and each signal consistng of an impulse of current of 'a sixth frequency followed within a predetermined interval 4of time bv an impulse of current of said fourth frequency, relay means operatively responsive to an `enablement signal preceding each' said train of signals, said enabling signal consisting of an impulse of current of said fifth frequency followed within a predetermined interval of time by an impulse of currentI of said fourth frequency, relay means operatively responsive to a signal consisting of said enablement signal followed by an impulse of current of said sixth frequency, and relay means operatively responsive to a signal consisting of an impulse of current of said fifth frequency followed within a predetermined interval of time by an impulse of current of said sixth frequency, and the signal receiving means at said other end of the line comprising relay means operatively responsive to a signal consisting of an impulse of current of said first frequency followed within a predetermined interval of time by an impulse of current of said second frequency, relay means operatively responsive to trains of signals, each train consisting of any desired number of signals and each signal consisting of an impulse of current of said third frequency followed within a predetermined interval of time first frequency, relay means operatively responsive to an enablement signal preceding each said train of signals, said enablement signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said first frequency, a signal consisting of said enablement signal followed by an impulse of current of said third frequency, and relay means operatively responsive to a signal consisting of an impulse of current of said second frequency followed within a predetermined interval of time by an impulse of current of said third frequency.

15.- In a signaling system, a plurality of sources of current, each source of a different frequency, a line, signal transmitting means connected to one end of said line, said signal transmitting means comprising signal relay means responsive to signals to be transmitted over said line, and means controlled by said signal relay means responsive to a train of selective signals for transmitting a` preparatory signal preceding the first selective signal, saidpreparatory signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency, and for transmitting an impulse of current of a third frequency immediately following the current of said second frequency and an impulse of current of said second frequency immediately following the current of said third frequency, and for transmitting an impulse of current of said third frequency followed by current of said second frequency for each succeeding selective signal of the train 16. In a signaling system, a plurality of sources oi' current, each source of a different frequency, a line, signal transmitting means connected to one end of said line, said signal transmitting means comprising signal relay means responsive to signals to be transmitted over said line, means controlled by said signal relay means responsive to a train of selective signals for transmitting a preparatory signal precedingl the first selective signal, said preparatory signal consisting of an impulse of current of a first frequency followed immediately by an impulse of current of a second frequency, and for transmitting an impulse of current of a third frequency immediately following the current of said second frequency and by an impulse of current of said i.

relay means operatively responsive to ,I

an impulse of current of said second frequency immediately following the current of said third frequency, and for transmitting an impulse of current of said third frequency followed by current of said second frequency for each succeeding selective signal of the train, and means comprising a delay network for delaying the transmission of each selective signal of a train for an interval of time equalA to that during which said preparatory signal is transmitted preceding the transmission of the signal .corresponding to the first selective signal of the train.

17. In a signaling system according to claim 15, signal receiving means connected to the other end of said line to receive the signals transmitted over the line from said signal transmitting means, said signal receiving means comprising relay means operatively responsive to a preparatory signal consisting of an impulse of current of said first frequency followed within a predetermined interval of time by an impulse of current of' said second frequency, and relaymeans rendered operative by the, operation of the relay means which is responsive to the. preparatory signal for responding to a train of selective signals each of which consists of current of said third frequency followed by current of said second frequency.

18. In a multioiiice signaling system, a first trunk line interconnecting a first and a second of said oiiices, anothertrunk line interconnecting said second and a third of said offices, a signal transmitter in said first oiiice and a signal receiver in said second oiiice associated with said first trunk line, means in saidI second oflice con- -necting said first line to said second line for the transmission of voice currents therebetween, said signal transmitter comprising means for transmitting a preparatory signal consisting of an impulse of current of a first signaling frequency followed immediately by an impulse of current of a second signaling frequency and for immediately thereafter transmitting an impulse of current of a third signaling frequency, said signal receiving means comprising means responsive to said preparatory signal for enabling a signal response to said impulse of current of the third signaling frequency, and means responsive to said preparatory signal for opening said connection between said first and second lines. thereby. to prevent the transmission of the impulse of current of said third signaling frequency over said second line.

19. In a signaling system according to claim 16, signal receiving means connected to the other end of said line to receive the signals transmitted over the line from said signal transmitting means, said signal receiving means comprising relay means operatively responsive to a preparatory signal consisting of an impulse of current of said first frequency followed within a predetermined interval of time by an impulse of current of said second frequency, and relay means rendered operative by the operation of the relay means which is responsive to the preparatory signal for responding to a train of selective signals `each of which consists of current of said third frequency followed by current of said second frequency.

NEAL L. NEWBY. HENRY E. VAUGHAN. 

